The jury trial of Hayden Smedley began in the ACT Supreme Court on Tuesday with the 21-year-old pleading not guilty to a charge of engaging in sexual intercourse without consent.

Opening the Crown case, prosecutor Keegan Lee told jurors Mr Smedley had matched with the alleged victim on the Bumble dating app in March last year.

Mr Lee said the girl's profile indicated she was 18, but she quickly told Mr Smedley she was in fact a year younger.

He said the pair had switched to communicating via Snapchat, and eventually agreed to meet and have sex at Mr Smedley's home.

"Let's bang," Mr Smedley allegedly wrote in one message ahead of the pair's first in-person meeting.

Mr Lee said that meeting happened on April 30 last year, when Mr Smedley and the alleged victim had what was initially consensual sex at the accused's townhouse in Gungahlin.

He said the pair stopped at one stage after the alleged victim indicated she was in pain.

But Mr Lee said Mr Smedley then told her: "I'm not done with you yet."

The prosecutor told the jury Mr Smedley asked the girl to perform oral sex on him, but she refused.

Mr Smedley allegedly responded with words to the effect of: "I'll make you suck my penis. You won't like it. That's why it's called rape."

According to Mr Lee, the accused then had penetrative sex with the girl despite her telling him to stop and at one point starting to cry.

He said that around this stage, Mr Smedley told the girl something like: "If you enjoy it, it's not rape."

The alleged victim eventually left Mr Smedley's home, and Mr Lee said she was physically trembling to the extent she had trouble opening her car door.

He told the jury she had immediately phoned a family member, "crying hysterically" and saying: "I told him to stop, but he didn't."

"The complainant felt violated," Mr Lee said.

"She felt physically sick, like she needed to vomit."

The prosecutor told jurors a subsequent medical examination revealed the alleged victim had suffered "a genital injury".

Defence barrister James Sabharwal did not give an opening address.

But Mr Lee said he expected Mr Smedley would claim any references to rape were just jokes, and that all sexual activity with the alleged victim had been consensual.

In a police interview played to the court later on Tuesday, the girl told investigators Mr Smedley had spoken in "a baby voice" when he allegedly made the comments about rape.

"I thought he was joking because afterwards he said, 'Oh, you should have seen your face'," she said.

"But then I thought, 'Who jokes about that?'"

She also told detectives Mr Smedley had sent her a Snapchat message with the caption "cutie" a short time after she left his home.

Justice Michael Elkaim told jurors the trial was expected to take three or four days.

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